Systematic errors should be included in spectral fitting since uncertainties in OSSE response may be larger than statistical uncertainties for bright sources. Scan angle dependent background systematics will also be important in many nonstandard pointing configurations.
Modeling on the "XSPEC standard", systematic errors, when available, are added in quadrature to the statistical errors in FITIT.PRO prior to fitting. Thus, the fit uncertainties and the deconvolved photon spectra reflect the larger uncertainties. Any fitting done outside the fitit environment needs to incorporate this quadrature summing of systematic and statistical errors to achieve the same result. NO CHANGES are made in DO_FOLDANAL.PRO or FFOLD.PRO.